This invention relates to tape transports and in particular to the control of a supply reel in a tape transport for regulating the tension in a magnetic tape for which the transport provides movement in a tape path extending around a cylindrical guide drum by means of which tape is guided in a helical path for scanning by a recording or playback head.
The need to regulate the tension in a magnetic tape in a tape transport is well-known, particularly when the transport forms part of a machine for recording signals on magnetic tape or playing back signals from such a tape. The stretchability of magnetic tape is notorious and is particularly susceptible to changes in temperature and humidity. The control of the tension in the tape is particularly important, because its variation affects the physical wavelengths of signals recorded on the tape and thereby causes undesirable variation in the frequencies played back from the tape and tends to cause deterioration in the quality of a played back signal.
It is well-known to provide means for sensing the tape tension in a tape path extending between a guide drum and, for example, a supply reel. Typically the means for sensing the tape tension comprises means for forming a loop of tape and for measuring the tape tension in that loop. A signal representing the tape tension may be used to control, in known manner, a motor driving the supply reel so as to tend to maintain the tape tension substantially constant. For this purpose it is known to provide a pivoted arm which carries a guide roller around which the tape path extends to form a loop so that variation in the tape tension causes pivoting of the arm. The pivoting can be sensed to provide a signal representing the tape tension and constituting, after comparison with a reference signal, an error signal for driving a servo amplifier for the motor which drives the reel. It is also known to correct for variations in tape tension by servomechanically controlling a take-up reel in accordance with detected tension errors and variations in the load experienced by a capstan disposed in the tape path between the take-up reel and the scanner. Although control of the loop tension in a buffer loop is an important feature of most tape transports, in order to ensure that a capstan driving the tape longitudinally is not loaded by the inertia of the tape reel and to ensure that the tape reel does not outrun the capstan, ordinary arrangements do not provide compensation for variation in tape tension at the scanner drum itself. One of the difficulties in doing so is the impracticability of monitoring the tape tension at or across the guide drum directly.
It is one object of the present invention to provide an improved tape transport.
It is another object of the present invention to provide compensation for variation in tension of a tape extending around a cylindrical guide drum in a tape transport for a video tape recorder.